Mycoplasmas are a group of microorganisms characterized by their small size and lack of a cell wall. A mycoplasma cell is bounded by a membrane, the chemical composition of which is similar to that of mammalian cells. Because of the difference between mycoplasmas and bacteria, antibacterial agents are not necessarily also effective against mycoplasmas. As the role of mycoplasmas in the aetiology of human, animal and plant diseases is more and more recognized, the fact that the number of chemotherapeutics active against these organisms is very limited makes the search for effective compounds worthwhile.